Since it's your mother's machine, you'll have a headstart if you already know how to use it.
If you can already sew with the machine, and don't need to be rescued every time you sew, I think you can pretty much jump into a beginner's sewing pattern. Instead of a teacher, buy a good reference book (reader's digest book is pretty popular) and join an active, non-lolita sewing group (usually has better variety). Read the posts in the group, usually someone will talk about the importance of pressing or ask about bias stuff occassionally, so you can learn things by lurking. Stick with simpler non-lolita patterns first, basic shift dresses and tunic patterns are far simpler to make. Then work your way up to dresses and blouses after that.
If you have no idea what to do with the machine, find the manual (actually you should keep the manual anyway, there's usually important stuff in it), schedule a session with your mom and see how far you can go. Once you can sew accurate lines, try some tote bag/pillow cases. Then, as above, jump right into a simple beginner's pattern, buy a book, join a group. Probably take you an hour to work out how to work the machine, most tote bags can be done in a few hours. Yes, you can go from zero to simple pattern overnight.
If you're having problems with the machine even with the manual, either the machine needs servicing, or you need lessons to help you remember what to do, or maybe both. You can seriously fuck up a machine if you don’t know how to use it, so this is one you do need help with.
I guess it sounds like I’m stressing machine use. I find that most beginner patterns are actually pretty thorough. You just need to follow instructions and not be too sloppy or skip over too many steps thinking you don’t need it, and the result is usually pretty good. And where the pattern is lacking, the book and the sewing group can usually help out. So give things a try and only look for a teacher if you get stuck.